Wide band amplifier and modulation system



e 25 1940- H. A. WHEELER WIDE BAND AMPLIFIER AND MODULATION SYSTEM Filed Aug. 16, 1938 2 Sheets-Sheet l H ROLD A WHEEL R ATTORNEY 31111@ 25 1940i l H.v A. WHEELER 2,205,738

WIDE BAND AMPLIFIER AND MODULATION SYSTENL l y Filed Aug. 1e, 195s' y2 sheets-sheet 2 aff mi 'N9 INV ' ATTORNEY Panarea' .im 2s, 1940 `UNITED sTATEsl PATENT OFFICE AMPLIFIER AND MODULATION SYSTEM Harold rWheelenrGreat Neck, N. Y., assignor to 4llazeltine Corporation, a corporation of Dela- Ware Application August 1e, 193s, serial No. 225,141

14 claims.

reactance termination at one end thereof have been utilized to maintain a predetermined value of transfer impedance substantially uniform over a wide bandof frequencies across one or more pairs of terminals of a coupling network. The principles and theoretical relations underlying dead-end filters of this type may be described most simply by reference to a nondissipative wave iilter of the constant-k type. Such a lter may be assumed to have an infinite number of sections or to consist of a finite number of sections terminated with `its image impedance to procure the same characteristics. 'Ihe input impedance of such a filter is uniform over the pass band if the input termination is full-shunt or full-series, as distinguished from the usual midshunt or mid-series termination. The input impedance is the iterative impedance measured in parallel with a full-shunt arm or in series with a full-series arm, as distinguishedfromtheconventional image impedance measured at midshunt or mid-series. This input impedance may be utilized as a two-terminal coupling impedance, the remainder of the iilter serving merely as a passive dead-end supplementary network utilized to build up the desired uniform impedance.

For example, any such lter of finite total band width can be arranged to include as its ful1shunt arm a capacitance of the value C=2/RAw, in which R is the mid-band image impedance and Aw is the total width of the pass band in radians per second. The uniform full-shut iterative im pedance across the capacitance C has the magnitude R=2/C'Aw. This relationship expresses the theoretically maximum value of impedance that can be maintained across the capacitance C throughout frequency bands of total width Aw. In the case of a simple low-pass filter, the value of R is twice the reactance of the capacitance Cd at the cuto frequency.

'111e deadfend lter may be utilized also as a.

' four-terminal network, thatis, a lter compris- (Cl. 17g-171.5)

ing an active portion and a conuent portion. In general, each of the dead-end terminal devices connected to the lter is limited in performance, over a wide frequency band, by either shunt susceptance or series reactance. Four-terminal networks may be employed which utilize the aboverecited principles for maintaining a predetermined uniform impedance across shunt susceptance, or a predetermined uniform admittance through series reactance, over a wide band of frequencies. The total susceptance or reactance of the circuits to be coupled is divided into smaller component portions connected in different sections of a lter, so that the impedance or admittance of the lter is limited, not by the total, but by the greatest indivisible portion of the undesired react'ance or susceptance. Coupling networks of this general type are described and claimed in applicant's copending applications, Serial No. 203,595 filed April 22, 1938, Patent No. 2,167,134, July 25 1939 and No. 203,596, iled April 22, 1938, Patent No. 2,167,135, July 25. 1939. Two terminal networks using similar `principles are described and claimed in applicants copending applications Serial No. 203,597 filed April 22, 1938, Patent No. 2,167,136, July 25,. 1939 and No. 203,598 filed on April 22, 1939, Patent No. 2,167,137, July 25, 1939. Certain of the prior art disclosures utilizing a network of the type under discussion, however, have been such as to require an appreciable amount of power to be dissipated in the dead-end termination of the lter; for example, it has been proposed to operate several tubes in parallel, their input and output terminals being staggered along input and output dead-end filters so that only the capacitance of one set of terminals of each tube limits the impedance of each iter section. The total phase shift of each section of the iilters is such that, when the signal carrier wave has a frequency equal to the mid-frequency of the pass band of the filter, so that the major portion of the power is concentrated in the middle of the pass band, the major portions of the currents delivered to the dead-end termination oi the output lter by the several parallel tubes are in phase and maximum power is dissipated therein.

Dead-end filters having a plurality of pairs of terminals have also been utilized in arrangements for coupling a band-pass signal-translating channel of a modulated-carrier signal translating system to a low-pass signal-translating channel. For example, it has further been proposed to operate a plurality of vacuum-tube detectors in parallel between a band-pass care tier-frequency signal-translating channel and a low-pass modulation-frequency signal-translating channel, each of the channels comprising as' a coupling network a dead-end filter having a plurality of pairs of terminals. Arrangements of the prior art, however, have been such that the phase-shift frequency characteristic of the low-pass signal-translating channel has been, over the pass band, of a slope similar to that of the band-pass signal-translating channel only where the low-pass band was half the width of the band-pass band, as for double-sideband operation.

It is an object of the invention, therefore, to provide anew and improved coupling network comprising shunt capacitance across which there is maintained a maximum and preferably uniform value of transfer impedance over a wide band of frequencies and in which useless dissipation is minimized.

It is another object of the invention to provide an amplifier utilizing a dead-end filter of the type described having a full-shunt termination at the active end thereof, in which the dead-end losses are a minimum.

It is a further object of the invention to provide a wind-band carrier-frequency translating system comprising a dead-end filter as a coupling network, in which the carrier frequency is so related to the pass band of the filter that the deadend losses in the filter are a minimum.

It is still another object of the invention to provide a wide-band signal-translating system comprising a low-pass signal-translating channel coupled to a band-pass signal-translating channel including a dead-end filter coupling network, in which the pass bands of the two channels are equal and the phase-shift frequency characteristics of the two channels are similar over the pass band.

In accordance with a preferred embodiment of the invention, there is provided in a modulatedcarrier` signal-translating systeml a signal-translating channel adapted to be energized by a source of carrier-frequency signals and including input and output circuits, a, coupling network comprising a dead-end filter having a resistance termination at its dead end. Each of the above-merrtioned input and output circuits is coupled with the lter at a junction of the lter separated from the dead end by at least one half-section of the filter. The carrier frequency of the source is located substantially at one edge of and within the pass band, whereby the carrier-frequency component is not substantially attenuatedbetween the input and output circuits, while the carrierfrequency component is substantially attenuated between the input circuit and the resistance termination.

Also in accordance with a preferred embodiment of the invention, there is provided in a modulated-carrier signal-translating system, a signal-translating channel including a plurality of phase-displaced input circuits and an output circuit. The channel includes a coupling network comprising a dead-end filter having a resistance termination at'its dead end and the above-mentioned input circuits are coupled with the lter at electrically-spaced junctions thereof remote from the dead end. The output circuit is coupled to the filter at a point more remote from its dead end than the above-mentioned junctions, whereby respective paths through successive input circuits to said output circuit include a decreasing number of sections of the lter and successive paths from the input circuits to the output deadend resistance include an increasing number of sections of the filter. Thecarrier frequency of the system is located within the pass band of the lter and so related with the transfer characteristics of the iilter that minimum power is dissif pated in the above-mentioned dead-end resistance termination.

Also, in a preferred embodiment of the invention, input and output dead-end filter networks are utilized in low-pass and band-pass signaltranslating channels, respectively, between which are coupled a plurality of vacuum tubes operating in parallel. 'I'he dead-end ltes are so designed that the-signal-translating channels comprising the dead-end filters have similar phase-shift frequency characteristics and equal band-widths; that is, over the pass band of the system, each of the signal-translating channels has the same total phase shift and band-width, so thatthe slopes of the phase-shift frequency characteristics are nearly the same in the two channels. y

For a better understanding of the invention, together with other and.' further objects thereof, reference is had to the following description taken in connection with the accompanying drawingsy and its scope will be pointed out in the appended claims.

Fig. la of the drawings shows an embodiment of the invention utilizing a plurality of vacuum tubes in parallel as a coupling between band-pass signal-translating channels; Fig. 1b' shows the phase-shift frequency characteristic of the system of Fig. la; Fig. 2a illustrates an embodiment of the invention utilizing a plurality of vacuumtube modulators as a coupling between' a lowpass signal-translating channel and a band-pass signal-translating channel; Fig. 2b illustrates the phase-shift frequency characteristics of the signal-translating channels of Fig. 2a; Fig. 2c represents certain characteristics of the system of Fig. 2a when the carrier frequency is located at one edge of the pass band of the band-pass channel; Fig. 2d illustrates certain characteristics of the circuit of Fig. 2a when the carrier frequency is located in the center of the pass band of the bandpass signal-translating channel; and Fig. 3 illustrates another embodiment of the invention in a band-pass channel. ,x

Referring now more particularly to Fig. la, there is shown a band-pass modulated-carrier signal-translating system comprising three stages of amplification including vacuum tube III in the first stage, tubes II and I2 coupled in parallel in the second stage, andy tube I3 in the third stage.

'Ihe system has a pair of input terminals I4 and a pair of output terminals I5. Dead-end filters, using the principles described in detail in the above-mentioned copending applications, are utilized to couple the output circuit of vacuum tube I0 to the input circuits of vacuum tubes II. and I 2 and to couple the output circuits of vacuum tubes II and I2 to the input circuit of vacuum tube I3. These lters are designatedgenerally as I6 and I1, respectively. Each of the filters I6 and I'I effectively comprises a plurality of modified' constant-k sections, an m-derived section,

and a resistive terminating impedance which matches the image impedance of the m-derived section over the pass band of the system. Certain inductances of filters I6 and I1 have been replaced by equivalent transformer elements and the interelectrode capacitances of tubes Ill, I I and l2 provide mid-shunt capacitances for the nlters at the junctions to which they are connected', as

aaowrss the filter, the image resistance of which is matched over the pass-band by resistance element 24. The remaining shunt inductances of filter I6 are inductances 25 and 26, while the shunt condensers of the filter are 21, 28, 29, 30, 3| and 32. I

The output filter I1, utilized for coupling the output circuits of tubes II and I2 to the input circuit of tube I3, is generally similar to vfilter I6 with the additional feature that an intermediate shunt element included in inductance 39 and condenser is provided as a termination for'filter I1 at the activeend thereof, in a manner described a nd claimed in the above-mentioned copending/applications Thus, filter 'I1 includes transformers 33, 34 and 35, the windings of which provide-equivalent inductance elements for modified constant-k sections, and transformer 36, the windings of which provide-equivalent. inductance elements for an m-de'rivedsection having an image impedance which is approximately matched over the pass band of the system by resistor 31. The remaining inductances offllter I1 are shunt inductances 3liande39f e shunt condensers of lten I1 are designated@y 4I, 42, 43, 44 and 45. Inoneembodiment of the invention, the circuit may be utilized-withasingle tube-iLiuhe I I being omitted from the circuit.

In Fig-ib, thereeis-showngthaphase-shift frequencybcharacteristic of each of the modified constent-k filter sections of filters I6 and I1, each filter having a total phase shift over the pass band of 1r, instead of 2n, as in conventional constant-Ic sections;

Considering now the operation of the circuit of Figs-iaith@ carrier-frequency power translated from the two tubes-ii-andI2 tothe ,dead-end resistor 3l of the Aoutput filter I1 canceisjout if the carrier frequency-isdn the middle 4oi-thef--pass band. This is apparent when separate baths from-input terminals i4 through tubes Il and it to resistor 3i are considered. Specifically, tubes il and it are coupled to filter i1 at electricallyvspaced junctions thereof remote from the dead end of the filter which includes resistor 3i, while the output terminals i5, tEi-of-filtergii are more remote from-its dead end than the junctions to which tubes Hand it. are coupled; The signal passing throughltube i2 to resistor 3l travels through two more filter sections than the signal through tube ii. Since each section of the filter has a phase shift of 1r/2 in mideband, the relative displacement-of the carrier-frequency currents translated to resistor 3i through the two paths is rr, so that the carrier-frequency power tends to cancel out;V that is. respective paths through suc- .l cessive input circuits to filter i? to the output terminals l5, it thereof include a decreasing number of sections ofthe iilter, while successive paths from the input circuits to the. output dead-end resistance 3l include an increasing number oi sections of the filter i'i. Since filter il is terminated at its active end to provide a maximum impedance over a wide range of frequencies across the active terminals thereof, as described in the above-mentioned copending applications, the iiiter is not ideally terminated', resulting in some reection at the active end, so that there is not an exact cancellation of power at the carrier frequency in resistor 3i.

It will be understood that any number of additional sections may be provided for filters I6 and I1 or that more than two tubes, connected in the manner shown, can be coupled between succeeding junctions of the filters. Furthermore, while in the arrangement described there results a cancellation of power at the carrier frequency in resistor 31 as between parallel-connected tubes II and I2, it will be understood that if an odd number of tubes is utilized, cancellation of power at the carrier frequency will result only if thel carrier frequency is displaced slightly from the midfrequency of the system.

Furthermore, the sections of the input and output filters may have any given phase-shift characteristic over the pass-band of the system and the carrier frequency may be so located with respect to the phase-shift frequency characteristics that cancellation of the power at the carrier frequency in the dead-end resistor 31 of the filter l1 results.

The system of Fig. la may be utilized in another way to minimize carrier dissipation in dead-end resistor 31 of the filter I1; that is, by operating Vthe system with the carrier frequency near the edge ofthe pass band, as would be done with single side-band operation. 'I'he m-derived termination, for which the windings of transformerA 36 provide the inductive elements, places a relatively high reactance in series with the dead-end resistor 31 (or a relatively low reactance in shunt therewith) at frequencies near the edge of the pass band. Therefore, locating the carrier frequency near the edge of the bandI greatly reduces the carrier power dissipated in resistor 31. The system just described may, of course, be operated with only one tube coupled between lters I6 and I1. Where several tubes are employed, a carrier frequency j.slightly within the band may be chosen, at Whichall carrier power cancels out by virtue of the first relations discussed above, andthe cancellation is non-critical because of the reduced carrier power in resistor 31 at frequencies near the edge of the band. These benefits are secured regardless of whether an even number or an odd number of tubes are utilized in parallel.

In Fig. 2a there` is shown a system similar in. many respects to that of Fig. 1a. The system of Fig. 2a is utilized to couple a low-pass channel, through parallel-operating modulator tubes, to a band-pass channel of the system. The system ltd thus comprises a first stage including a vacuum tube it', a second stage, including parallel-operating modulator tubes lI and I2', and a third stage including a vacuum tube i3. The bandpass output filter l'i of Fig. 2a is identical with that of Fig. 1a and corresponding circuit elements have been given similar reference numerals in the two iigures. The input filter 5t is of the lowpass type and comprises three constant-.7c sections including series inductance arms 5I, 52 and 53 and shunt capacitance arms 511i, 55, 56 and 51, capacitance elements 545, and 56 being shown in dotted lines to indicate that they arey comprised in whole or in part of the inherent interelectrode capacitances of the vacuum tubes coupled to the filter at these points. An m-derived half-section including an inductance 58 and, a capacitance 59 is provided for lter 50. The image impedance of the m-derived half section is approximately matched over the pass band of the system by terminating resistor EU. There are provided input terminals 6i for the low-pass section of the circuit and input terminals 62 for the bandmodulated-carrier signal which is coupled to output terminals I through the output filter I1. The input circuit coupled to input terminals 82 comprises a condenser 6l connected in parallel with inductances A.65 and 66. Inductances 85 and 68 are inductively coupled to inductances 61 and- 88 of the input circuits of vacuumtubes II' and l2', respectively. The carrier-frequency input to modulators I I' and I2' is applied with such polarity that the carrier-frequency outputs of the modulator tubes are coupled in the same phase to output terminals I6.

The circuit of Fig. 2a effectively provides an arrangement in which the slope of the phaseshift frequency characteristic of the low-pass input iilter 60 is approximately similar over the pass band to that of output filter I1. These characteristics are shown in Fig. 2b wherein curve A represents the phase-shift frequency charac- 'teristic of iilter 50 and curve B represents the phase-shift frequency characteristic of lter I1.

If only one sideband is to be employed in the f arrangements of the invention, it ispreferable f to locate the carrier at one edge of the pass band,.-

in which case it is desirable that the relative phase shift of the band-pass lter over the pass band should be the same as that of the low-pass iilter. This arrangement, in which the low-pass band width is equal to the band-pass band width and in which the relative phase shift over each pass band is 1r per section in each of filters 50 and I1, gives approximately the correct phase relations between the ymodulation-frequency signal and the modulation sideband signal components, regardless of where the carrier-frequency is located in the band. 'Ihe carrier frequency must be near the edge of the band, however, if the band-pass filter is to accommodate a width of sidebands as wide as the band width of the lowpass filter. These characteristics are indicated in Figs. 2c and 2d wherein Fig. 2c illustrates the arrangement in which the carrier frequency is located at the low-frequency edge ,f5 of the pass yband f5, f6 of the band-pass filter I1. The pass band of the'iow-pass filter su is indicated by O-f'r. Fig. 2d illustrates a low-pass band width of O-fa and a band pass from fe--io with the carrier frequency located at fu, themid-point of pass band fia-fio. Due to the difference between curves A and B of Fig. 2b, the desired relation between the phase-shift frequency characteristic of input filter 50 and that of the output filter I1 of Fig. 2a -is not exact but is sufficiently close if the number of tubes in parallel between the lters is not too great, for example, not .greater than four.

In Fig. 3, there is illustrated a modification of the circuit of Fig. 1a in which the single tube of each of the parallel channels is replaced by a driver tube and a power tube. Similar circuit elements in the two figures have been given identical reference numerals, the input filter I6 being identical with that of Fig. 1a. The output filter is similar to output filter I1 of IFig. la except for the termination thereof at the active end. Output filter 10 is terminated to provide an image impedance at output terminal which matches the image impedance of a uniform transmission line. Tubes II and I2 'of Fig. la.I have been replaced in the circuit of Fig. 3 by identical parallel channels each including a driver tube 16, the input circuitof which is coupled to accuse filter I8 in the manner above described, and a power tube 11, the output circuit of which is coupled to output filter 10 in a manner similar to that described for coupling the output circuits of tubes II and I2 of Fig. 1 to the output circuit oi 'lter I1. The output circuits of tubes 16 are coupled to the input circuits of tubes 11 by dead end coupling filters in accordance with the disclosures of th above-mentioned copending applications. Each of these lters comprises a plurality of modified constant-k sections, the inductance elements oi?v which are provided by the windings ci a transformer 18 and shunt inductance arms 19 and 80, and an m-derived halfsection, the inductance elements of which are provided by the windings of a transformer 8l. Shunt capacitance arms 83, 84, 85 and 86 are provided for the filters, condensers 85 and 86 being shown in dotted lines to indicate that they are comprised in whole or in part of the inherent interelectrode capacitances of tubes 16 and 11, respectively. The dead-end terminating resistor 81 of the coupling lter matches the image vantageous arrangement for the power output circuit of a transmitter, inasmuch as relatively small driver tubes 16, 16 can be utilized together with relatively large power tubes 11, 11. Power tubes are generally operated by driving the grids positive, in which case the grid loading operates as a shunt conductance at' the end of the coupling lter between the driver and power tubes. Therefore, conductance 88 may be proportioned in accordance with the disclosure of above-mentioned copending application, Serial No. 203,595.

It will be seen that, inasmuch as filter 10 is adapted to be ideally matched with a uniform line coupled to terminals 15, there is no reflection if the line is properly terminated at the other end. Cancellation of power in the dead-end terminating resistor 31 of filter 10 is then more exact than that obtained in dead-end resistor 3l of output filter I1 of Fig. 1a.

It will be understood that the above-described carrier-frequency. amplifier arrangements are particularly advantageous when employed in push-pull amplifiers, there being no difference in the principles involved so that detailed explanation thereof is deemed unnecessary. Furthermore, it will be understood that it is preferable to utilize tubes in the above circuits which have an anode resistance much higher than the impedance of the associated anode circuits whereby the signal voltage output of the tubes is minimized. This result is best obtained by using screen-grid tubes or high-mu triodes. If the tubes utilized do not have a screen grid, the grid-anode coupling capacitance should preferably be neutralized. 'Ihe most perfect type of neutralization and, therefore, the one which is preferred is the cross-neutralization of two tubes in push-pull relation in the same signal channel. Each of the While there have been described whatare at A present considered to be the preferred embodiments of thisl invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modications as fall-within the true spirit and scope of the invention.

`What is claimed is: Y

1. In' a modulated-carrier signal-translating system, a signal-translating channel adapted to be energized by a source of carrier-frequency signals and including input and output circuits, a coupling network comprising a dead-end filter having a resistance termination at its dead end, each of said input and output circuits being coupled with said lter,l at a junction of said lter separated from said dead end by at least one half-section of said-filter, the carrier frequency of said source being located substantially at one edge of and within the pass band, whereby the carrier-frequency component is not substantially attenuated between said input and output circuits while the carrier-frequency component is substantially attenuated between said input circuit and said resistance.

2. In a modulated-carrier signal-translating system, a signal-translating channel adapted to be energized by a source of carrier-frequency signals and including input and output circuits, a coupling network comprising a dead-end filter having a resistance termination at its dead end, each of said input and output circuits being coupled with said filter at a junction of said filter separated from said dead end by at least one half-section of said filter, said dead-end filter having an m-derived image impedance approximately matched by said resistance termination at its dead end, the carrier frequency of said source being located substantially at `one edge of and within the pass band, whereby the carrier-frequency component is not substantially attenuated between said input and output circuits while the carrier-frequency component is substantially attenuated between said input circuit andY said resistance.

3. In a modulated-carrier signal-translating system, a signal-translating channel adapted to be energized by a source of carrier-frequency signals and including input and output circuits, said output circuit comprising appreciable shunt capacitance tending to limit the response thereof over awide frequency range, a coupling network comprising a dead-end filter having a resistance termination at its dead end, said lter including said capacitance as a mid-shunt element thereof, each of said input and output circuits being coupled with said filter at a junction of said lter separated from said dead end by at least onehalf section of said filter, said dead-end filter having an m-dexived image impedance approximately matched by said resistance termination at its dead end, the carrier frequency of said source being located substantially at one edge of and within the pass band, whereby the carrierfrequency component is not substantially attenuated between said input and output circuits while the carrier-frequency component is substantially attenuated between said input circuit and said resistance.

4. In a modulated-carrier signal-translating system, `a signal-translating channel including two phase-displaced input circuits and an output circuit, a coupling network comprising a dead-end lter having a resistance termination at said dead end, said input circuits being coupled with said filter at electrically spaced junctions -thereof remote from said dead end, and said output circuit being coupled to said fllter at a point more remote from its' dead end than 5 Asaid junctions, whereby respective paths through successive -inputcircuits to said output circuit include a decreasing number of sections of said filter and successive paths from said input circuits -to said output dead-end resistance include an increasing number of sections ofv said lter, and the carrier frequency being located within the pass band of said filter and so related with the transfer characteristics of said filter that minimum power is dissipated in said dead-end 16 resistance termination.

5. In a modulated-carrier signal-translating system, a signal-translating channel including input and output circuits, input and output deadend filters, a plurality of vacuum tubes effectively 20 in parallel and coupling said circuits through portions of said filters, each'of said filters having a dead-end resistance termination, said tubes being coupled with each of said filters at electrically spaced junctions thereof remote from ysaid dead ends, each of said input and output circuits being coupled with its respective filter at a p oint more remote from its dead end than the said junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuits through successive tubes include increasing numbers of sections of one of said filters and a decreasing number of sections of the other filter and the respective paths from said input circuit to said output dead-end resistg5 ance through successive tubes include an increasing number of sections of both of said filters, and the carrier frequency being located within the pass band of said filters and so related with the transfer characteristics of said lters that mini-v an mum power is dissipated in the said dead-end resistance termination of the said output filter.

6. In a modulated-carrier signal-translating system, a signal-translating channel including input and outputcircuits, a coupling network comprising a dead-end lter having a resistance termination at its dead end, a plurality of vacuum tubes effectively in parallel and coupling said circuits through portions of said filter, said tubes being coupled to said filter at electrically spaced junctions thereof remote from said dead end, said junctions being displaced along said filter by por-l tions each having predetermined phase shift at a predetermined frequency within the pass band of said system, said output circuit being coupled with said filter at a junction of said filter more remote from said dead end than the junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuit through successive tubes include decreas- 00 ing numbers of sections of said filter and the respective paths from said input circuit to said output dead-end resistance through successive tubes include increasing numbers of sections of said filter, and the carrier frequency of said system being proportioned with respect to said predetermined frequency so that the total phase displacement through successive tubes from said input circuit to said dead-end resistance at said carrier frequency differ by 180 degrees, whereby 7'0 carrier frequency power therein tends to cancel out.

7. In a modulated-carrier signal-translating system, a signal-translating channel including input and output circuits, input and output bandpass deadend iters, a plurality of Avacuum tubes effectively in parallel and coupling said circuits through portions of said filters, each of said filters having a dead-end resistance termination. said tubes being coupled to said filters at electrically spaced junctions thereof remote from said. dead ends, said junctions being displaced along said filters by portions each having a 90 degree phase shift at a predetermined frequency withinu the nass band of said system, said input and output circuits being respectively coupled with said nlters at junctions of said filters more remote from said dead ends than the junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuits through successive tubes includey increasing numbers of sections of one of said lters and a decreasing number of sections of the other lter, the respective paths from said input circuit to said output dead-end resistance through successive tubes including an increased number of sections of both of said lters, and the carrier frequency of said system being equal to said predetermined frequency whereby the l.total phase'displacements through successive tubes from said input circuit to said output dead-end resistance at said carrier-frequency, diifer by 180 degrees, so that the carrier-frequencyrpower therein tends to cancel out.

8. In a modulated-carrier signal-translating system, a signal-translating channel including input and output circuits, input and output bandpass dead-end filters, an even number ofvacuum tubes eilectively in parallel and coupling said circuits through portions of said filters, said llters each having a dead-'end resistance termination, said tubes being coupled with said filters at junctions of said filter separated from said dead ends, said junctions being electrically displaced along eachyiilter by portions having zero to 180 degrees phase shift over the pass band of said system, said input and output circuits being respectively coupled with the said lters at junctions of said illters more remote from said dead ends than the said junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuit through successive tubes include increasing numbers of sections of one of said filters and a decreasing number of sections of the other of said iilters, the respective paths from said input circuit to the output dead-end resistance through successive tubes including an increasing number of sections of both of said filters, and the carrier frequency of said system being located at the midfrequency of said pass band, whereby the total phase displacement through successive tubes from said input circuit to said dead-end resistance at said carrier frequencies diiers by 130 degrees so that the carrier-frequency power therelin tends to cancel out.

' input and output circuits, input and output deadend lters, a plurality of vacuum tube modulators effectively in parallel and coupling said circuits through portions of said filters, one of said iilters being of a low-pass type and the other of said filters being of a band-pass type, said filters having pass bands of equal width, each of said lters having a dead-end resistance termination, said tubes being respectively coupled to said filters at electrically spaced junctions thereof remote from said dead ends, said input and output circuits being coupled with the respective lters at `iunctions of said lters more remote from said dead ends than the said junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuits through successive tubes include increasing numbers of sections v of one of said lters and decreasing numbers of sections of the other iilter, the respective paths from said input circuit 'to saidoutput dead-end resistancev through successive tubes including an increased number of sections of both of said lters, and said :Iun'ctionsbeing displaced along eachviilter by a portion having zero to 180 degrees phase shift over the pass band of said system, whereby the total phase shift from said input circuit to said output circuit through successive tubes has the same average value over said pass band.

10. In a modulated-carrier signal-translating system, a 'signal-translating channel including input and output circuits, input and output deadend filters, a plurality of modulator vacuum tubes effectively jin parallel and coupling said circuits through portions of said illters, said input filter being of a low-pass type and said output filter being of a band-pass type, said filters having pass bands of equal width, each of said filters havinga dead-end resistance termination, said tubes being connected with said iilter'at elec-A trically spaced junctions thereof remote from saidl deadends, said input and output circuits being respectively coupled with said filters at Junctions vof said filters more remote from said dead ends than said junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuits through successive tubes include an increasing number of sections of one of said lters and a decreasing number of sections of the other of said lters, the respective paths from said input circuit to the dead end of said output filter through successive tubes including an increasing number of sections of both -of said iilters, and a carrierfrequency circuit coupled to input circuits of said tubes with such relative phase as to be coupled through each tube to said output circuit in the same phase, the frequency of said voltage being ilted within the pass band of said band-'cass 11. In a modulated-carrier signal-translating system, a signal-translating channel including input and output circuits, input and output dead-end filters, a plurality of modulator vacuum tubes effectively coupling said circuits through portions of said filters, said input lter being of a low-pass typel and said output iilter being of a band-pass type, said lters having pass bands of equal width, each of said filters having a dead-end resistance termination, said tubes being respectively connected to said filters at electrically spaced junctions thereof remote fromsaid dead ends, said input and output vcircuits being coupled with the respective iilters at junctions of said filters more remote from said dead ends than said junctions to which said tubes are coupled, whereby the respective paths from said input to said output circuits through successive tubes include an increasing number of sections of one of said iilters and a' decreasing number of sections of the other of said lters, the respective paths from said input circuit to said output dead-end resistance through successive tubes including an increasing number of sections of both of said filters, and a source of carrier frequency voltage coupled through said input #circuit to said tubes in such phase as to be c ou- 7-5 pled through each tube to said output circuit in the same phase, .the frequency of s aid voltage being located at one edge and just within the pass band of said output filter, whereby the band-pass output iilter passes all of one sideband corresponding to all modulation frequencies of the band of said low-pass input filter.

12. In a modulated-carrier signal-translating system, a signal-translating channel including a plurality of phase-displaced input circuits and an output circuit, a coupling network comprising a dead-end filter having a resistance termination at said dead end, said input circuits being coupled with said filter at electrically spaced junctions thereof remote from said dead end, and said output circuit being coupled to said filter at a point more remote from its dead end than said junctions, whereby respective paths through said successive input circuits to said output circuit include a decreasing number of sections of said filterv and successive paths from said input circuits to said output dead-end resistance include an increasing number of sections of said filter, and the carrier frequency being located within the pass band of said filter and so related to the transfer characteristics of said filter that minimum power is dissipated in said d ead-end resistance termination.

13. In a modulated-carrier signal-translating system, a signal-translating channel including a plurality of phase-displaced input circuits and an output circuit, a coupling network comprising a dead-end filter having a resistance termination at said dead end, each of said input and output circuits being coupled with said filter at a junction of said lter separated from said dead end by at least one half-section of said filter, said input circuits being coupled with said filter at electrically spaced junctions thereof and said output circuit being coupled to said filter at a point more remote from its dead end than said junctions, whereby respective paths through successive input circuits to said output circuit include a decreasing number of sections of said filter, and successive paths from said input circuits to said output dead-end resistance include an increasing number of sections of said filter, and the carriery frequency being located Within the pass band of said filter and so related to the transfer characteristics of said filter that minimum power is dissipated in said dead-end resistance termination.

14. In a modulated-carrier signal-translating system, a signal-translating channel including a plurality of phase-displaced input circuits and an output circuit, a coupling network comprising a dead-end filter having a resistance termination at said dead end, a plurality of` vacuum tubes having output capacitance, each of said input circuits being coupled with said lter through one of said vacuum tubes at electrically spaced junctions thereof remote from said dead end. the said output capacitance of each tube comprising a substantial part of a shunt arm of said filter at the junction at which the particular vacuum' tube is coupled, said output circuit being coupled to said filter at a point more remote from its dead end than said junctions, whereby respective paths through successive input circuits to said output circuit include a decreasing number of sections of said filter and successive paths from said input circuits to said output dead-end resistance include an increasing number of sections of said filter, and the carrier frequency being located within the pass band f said filter and so related to the transfer characteristics of said lter that minimum power is dissipated in said.Y dead-end resistance termination.

HAROLD A. WHEELER. 

